JP3162531B2 - Lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte batteries using lithium as a negative electrode active material have attracted attention as high energy density batteries, and manganese dioxide (MnO ₂ ) has been used as a positive electrode active material.
Fluorocarbon [(CF ₂ ) _n ], thionyl chloride (SOCl
Primary batteries using ₂ ) and the like are already widely used as power supplies for calculators, watches, and as backup batteries for memories.

Further, in recent years, as various electronic devices such as VTRs and communication devices have become smaller and lighter, the demand for a secondary battery having a high energy density has increased as a power source for these devices. Research on secondary batteries is being actively conducted.

A lithium secondary battery uses lithium as a negative electrode and uses propylene carbonate (P) as a solvent as an electrolyte.
C), 1,2-dimethoxyethane (DME), γ-butyrolactone (γ-BL), tetrahydrofuran (TH
F) in a non-aqueous solvent such as LiClO ₄ , LiBF ₄ , Li
A non-aqueous electrolytic solution in which a lithium salt such as AsF ₆ is dissolved or a lithium ion conductive solid electrolyte is used. As the positive electrode active material, TiS ₂ , MoS ₂ , V ₂ O ₅ , V ₆ O ₁₃ ,
The use of compounds that undergo a tohochemical reaction with lithium, such as MnO _2, has been studied.

[0005] However, the lithium secondary battery as described above has not yet been put to practical use. The main reason for this is that the charge / discharge efficiency is low and the number of times that charge / discharge can be performed (cycle life) is short. It is considered that this is largely due to the deterioration of lithium due to the reaction between the lithium of the negative electrode and the non-aqueous electrolyte. That is, lithium dissolved in the non-aqueous electrolyte as lithium ions at the time of discharge reacts with the solvent at the time of deposition at the time of charging, and its surface is partially inactivated. Therefore, when charge and discharge are repeated, lithium precipitates in a dendritic (dendritic) or small spherical shape, and further, phenomena such as detachment of lithium from the current collector occur.

[0006] Therefore, by using a carbonaceous material that absorbs and desorbs lithium, such as coke, a resin fired body, carbon fiber, and pyrolysis gas phase carbon, as the negative electrode incorporated in the lithium secondary battery, It has been proposed to improve the reaction with a non-aqueous electrolyte and the deterioration of the negative electrode characteristics due to the precipitation of dendrites.

[0007] In the negative electrode of a lithium secondary battery using a carbonaceous material, the above-mentioned layers are mainly formed in a portion of a carbonaceous material having a structure in which hexagonal mesh layers composed of carbon atoms are stacked (graphite structure). It is considered that charging and discharging are performed by lithium ions entering and exiting between the portions. Therefore, it is necessary to use a carbonaceous material with a somewhat developed graphite structure for the negative electrode of a lithium secondary battery.However, if a carbonaceous material obtained by pulverizing a graphitized giant crystal is used as a negative electrode in a non-aqueous electrolyte, The non-aqueous electrolyte is decomposed, and as a result, the capacity of the battery and the charge / discharge efficiency are reduced. In particular, when the battery is operated at a high current density, the capacity, charge / discharge efficiency, and voltage at the time of discharge significantly decrease. Further, as the charge / discharge cycle progresses, there is a problem that the crystal structure or microstructure of the carbonaceous material is destroyed, the ability to occlude and release lithium is deteriorated, and the cycle life is poor.

[0008] Further, even in the case of graphitized carbon fibers, the non-aqueous electrolyte solution is decomposed when powdered, and the performance as a negative electrode is greatly reduced as in the case of using giant crystal powder. Had a point.

On the other hand, in the case of carbonized products such as coke and carbon fiber having a low degree of graphitization, although the decomposition of the solvent can be suppressed to some extent, there are problems such as low capacity, low charge / discharge efficiency, and poor cycle life. are doing.

Conventionally, JP-A-62-268058 and JP-A-2-2-268058
No. 82466, JP-A-4-61747, JP-A-4-115458
JP, JP-A-4-184862, JP-A-4-190557 and the like to control the degree of graphitization of various carbonized and graphitized, and has the optimal graphite layer structure parameters Although a carbon material and a battery configuration of a battery using the same as a negative electrode have been proposed, a lithium secondary battery having sufficient characteristics has not been obtained.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a lithium secondary battery having high capacity and excellent cycle characteristics such as cycle life.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a positive electrode comprising, as an active material, a lithium metal compound mainly containing at least one metal selected from cobalt, nickel, manganese, vanadium, titanium, molybdenum or iron. ,
Occludes and releases lithium ions, 700 ° C by differential thermal analysis
As described above, the peak intensity ratio (P ₁₀₁ / P ₁₀₀ ) of the (101) diffraction peak (P ₁₀₁ ) and the (100) diffraction peak (P ₁₀₀ ) of the graphite structure having an exothermic peak and X-ray diffraction is 0.7.
A lithium secondary battery comprising a negative electrode containing a carbonaceous material powder of 2.2 or more and a non-aqueous electrolyte, wherein the ratio of the thickness of the positive electrode to the thickness of the negative electrode is 2: 1 to 0.9: 1. And a ratio of the weight per unit area of the positive electrode to the weight per unit area of the negative electrode is from 4: 1 to 2: 1.

[0013]

[0014]

The carbonaceous material of the negative electrode according to the present invention has an intensity ratio P ₁₀₁ / P ₁₀₀ of the (101) diffraction peak (P ₁₀₁ ) and the (100) diffraction peak (P ₁₀₀ ) by X-ray diffraction of a graphite structure.
Is not less than 0.7 and not more than 2.2. The (101) diffraction peak (P ₁₀₁ ) and (100) by X-ray diffraction in this specification.
Peak intensity ratio of the diffraction peak _{(P 100) (P 101 /} P 100)
Is obtained from the peak height ratio.

The peak intensity ratio (P ₁₀₁ / P ₁₀₀ ) is within the above range.
The carbonaceous material in the box has a moderately developed graphite structure.
The hexagonal mesh layers stacked in the graphite structure
It is considered that there is moderate displacement, twist, and angle
You. The hexagonal mesh layers stacked in this way
If it has misalignment, twist, or angle,
Diffusion of lithium ions in
Shows the property of reversibly occluding and releasing lithium ions
It is considered something. Also, such carbonaceous materials are
The graphite structure collapses due to occlusion and release between muons
It is considered difficult to handle. Occlusion of lithium ions between layers
・ If the graphite structure collapses due to release, lithium ion absorption
Reduced storage / release amount and active surface for non-aqueous solvent
Is thought to occur, and the solvent is likely to undergo reductive decomposition. Ma
In addition, broken fine crystals also simultaneously reduce and decompose solvents.
it is conceivable that.

The peak intensity ratio (P ₁₀₁ / P ₁₀₀ ) is higher
Carbonaceous materials exceeding the above values (for example, natural graphite, etc.)
With the development of graphite structure, misalignment, twist, and angle of the hexagonal mesh layer
Are those not small. Such carbonaceous materials are especially
Under charge / discharge conditions (for example, 0.5 mA / cm ² or more)
The amount of occluded and released lithium ions is rather reduced.
In addition, the surface is active against a non-aqueous solvent, and the solvent is
It is thought that reductive decomposition is likely to occur.
The capacity, charge / discharge efficiency, and cycle life characteristics decrease.

On the other hand, the peak intensity ratio (P ₁₀₁ / P ₁₀₀ )
Carbonaceous materials smaller than the above range are those with undeveloped graphite structures.
Substantial substances are often mixed in carbonaceous substances, and the displacement of hexagonal mesh layer,
The twist and angle are too large.
Those with little reversible occlusion / release between hexagonal mesh layers
It is considered that the capacity, charge / discharge efficiency,
And the cycle life characteristics decrease. Also, peak intensity ratio
Those values of (P ₁₀₁ / P ₁₀₀₎ is 0.8 to 1.8
However, battery capacity, charge / discharge efficiency, and cycle life characteristics
Improved and more preferred.

The carbonaceous material of the negative electrode according to the present invention is analyzed by X-ray analysis.
Average spacing (d ₀₀₂ ) of (002) plane obtained by
Desirably, it is 0 nm or less. The carbonaceous material having the above range has a graphite structure developed to some extent, and the interval between the layers of the hexagonal mesh layer is suitable for a smooth absorption / release reaction of lithium ions. If the above range is not satisfied, the capacity will decrease, and the overvoltage during charging and discharging will increase,
The flatness of the voltage at the time of discharging the battery is reduced. More preferably, (d ₀₀₂ ) is 0.3358 nm or more and 0.3440 nm or less. A more preferred range is from 0.3359 nm to 0.3380 nm.

The carbonaceous material of the negative electrode according to the present invention has an exothermic peak at 700 ° C. or higher by differential thermal analysis. The value of the exothermic peak by differential thermal analysis is a measure of the carbon-carbon bonding force of the carbonaceous material. A carbonaceous material having an exothermic peak in this range has a property in which a graphite structure is appropriately developed and lithium ions are reversibly inserted and released between layers of a hexagonal mesh layer in the graphite structure. Further, it is considered that the carbonaceous material has a small amount of amorphous carbon active in the non-aqueous solvent.

The exothermic peak only exists below 700 ° C.
If the carbonaceous material is not
Since it is present in carbonaceous materials, it has a graphite structure of lithium ions.
Reversible entry and exit between hexagonal mesh layers between layers
It is considered something. In addition, fine powders active against non-aqueous solvents
A large amount of amorphous carbon is present, and non-aqueous solvents are easily reduced and decomposed
It is thought to be.

That is, As carbonaceous material used for the negative electrode of a lithium secondary battery, the graphite layer structure is developed moderately, there have
Furthermore, by using a stack of hexagonal mesh layers in the graphite structure that have an appropriate shift, twist, and angle, the lithium ion occlusion and
The release reaction proceeds smoothly and the amount of active carbon in the non-aqueous solvent is small, so that reductive decomposition of the non-aqueous solvent is suppressed.

The value of the exothermic peak in the above differential thermal analysis is more preferably 800 ° C. or more. More preferably, the temperature is 840 ° C. or higher.
In the present specification, the values of the differential thermal analysis are measured under conditions of a heating rate of 10 ° C./min, a sample weight of 3 mg, and air.

[0024] The carbonaceous material of the negative electrode according to the present invention has X
By diffraction peak of (110) plane obtained by X-ray diffraction
The average length (La) of the crystallite in the a-axis direction of the graphite structure is 20 nm
It is preferably at least 100 nm. Also, (La)
Is more preferably 40 nm or more and 80 nm. What
Incidentally, it is obtained by X-ray diffraction in this specification (11
0) Crystallite in a-axis direction of graphite structure by diffraction peak of plane
Has an average length (La) of 0.89 when the form factor K of Scherrer's equation is 0.89.
Is the value when Note that the graphite structure of carbonaceous material
The ratio of the a-axis plane to the c-axis plane (La / Lc) is 0.5 to 2.0.
Preferably, there is. More preferably in the range of 0.5 to 1.5
It is good. Within this range, Li ion insertion
The response becomes smoother, and the utilization rate improves.

In the carbonaceous material having (La) in this range, the graphite structure is appropriately developed and the length of the crystallite in the a-axis direction is moderate, so that lithium ions can be intercalated between the hexagonal mesh layers. More easily, and the number of sites where lithium ions enter and exit increases, indicating that lithium ions can be absorbed and released more.

The carbonaceous material whose (La) exceeds 100 nm becomes a giant crystal, making it difficult for lithium ions to diffuse between the layers of the hexagonal mesh layer, and making it difficult to secure the amount of occluded and released lithium ions. In addition, the surface is active with respect to a non-aqueous solvent, and the solvent is liable to undergo reductive decomposition. Also, (L
It is considered that the carbonaceous material having a) of 20 nm or less has less reversible occlusion and release of lithium ions between the layers of the hexagonal mesh layer because the carbonaceous material with an undeveloped graphite structure is often mixed in the carbonaceous material. Can be

Further, the carbonaceous material of the negative electrode according to the present invention comprises X
Of crystallite in the c-axis direction obtained by X-ray diffraction (L
c) is preferably greater than 15 nm. More preferably, (Lc) is 20 nm or more and 100 nm or less. When (Lc) is in the above range, the graphite structure develops moderately and exhibits a property of reversibly occluding and releasing a large amount of lithium ions. In the present specification, the crystallite size (Lc) in the c-axis direction obtained by X-ray diffraction is such that the form factor K in Scherrer's equation is 0.
This is the value when 89 is set.

The data of the measurement by X-ray diffraction described in this specification all used CuKα as an X-ray source and high-purity silicon as a standard substance. (La), (d ₀₀₂ ), (L
c) was determined from the position of each diffraction peak and the half width. As a calculation method, a half-width midpoint method was used.

As a measure of the ratio between the graphite structure and the turbostratic structure constituting the carbonaceous material of the negative electrode according to the present invention, there is a Raman spectrum of the carbonaceous material measured using an argon laser (wavelength: 514.5 nm) as a light source. . In the Raman spectrum measured for the carbonaceous material, there are a peak derived from a turbostratic structure appearing around 1360 cm ^-1 and a peak derived from a graphite structure appearing around 1580 cm ^-1 . The peak intensity ratio, that is, the peak intensity (R at 1580 cm ^{-1 in} the argon laser Raman spectrum (wavelength 514.5 nm))
Ratio of peak intensity (R1) at 1360 cm ^{-1 to} 2) (R1
It is preferable to use a carbonaceous material having a value of / R2) of 0.7 or less.

Further, the carbonaceous material of the negative electrode according to the present invention has the following properties:
It is preferably 15 g / cm ³ or more. True density is a measure of the degree of graphitization. The carbonaceous material of the negative electrode according to the present invention preferably has a particle size distribution of 90% by volume or more in a range of 1 μm to 100 μm, and an average particle size of 1 μm to 80 μm. It is appropriate that the specific surface area of the N ₂ gas adsorbed by the BET method is 0.1 to 40 m ² / g. The carbonaceous material in the above range increases the packing density of the negative electrode, and at the same time, contains less carbonaceous material with a broken graphite crystal structure or amorphous carbon, which is active in the nonaqueous solvent, and reduces the decomposition of the nonaqueous solvent. Can be suppressed. Further, the carbonaceous material having a particle size of 0.5 μm or less in a particle size distribution of 5% by volume or less has further less carbonaceous material or amorphous carbon having a broken graphite crystal structure, and reduces reductive decomposition of a non-aqueous solvent. Conversely, the particle size distribution and, if the specific surface area measured by the BET method of N ₂ gas adsorption is too large, the content of the collapsed carbonaceous material containing and graphite crystal structure of amorphous carbonaceous material is increased, occur reductive decomposition of the solvent It will be easier. Further, the packing density of the negative electrode is reduced.

Also, the book The carbonaceous material of the negative electrode according to the invention is:
Those having a sulfur content of 1000 ppm or less (including 0 ppm) are preferred. Thereby, the amount of insertion and extraction of lithium ions is increased, and the reductive decomposition of the non-aqueous solvent is reduced.

This indicates that the carbon content of which the graphite structure has developed to some extent (shows an exothermic peak at 700 ° C. or higher by differential thermal analysis) has a low sulfur content of 1000 ppm or less (including 0 ppm). Thus, it is considered that the graphite structure has few defects, and as a result, the graphite structure is less likely to collapse, and the amount of occluded and released lithium ions increases. Therefore, the capacity, charge / discharge efficiency, and cycle life of the lithium secondary battery are increased. In addition, it is considered that the decomposition of the non-aqueous solvent and the inhibition of the electrode reaction due to the reaction of the non-aqueous solvent and the lithium ion with the sulfur or the sulfur compound are reduced, and the charge and discharge efficiency and the cycle life are improved. That is, when sulfur in the carbonaceous material reacts with lithium ions, LiS
To form a stable group such as-or a compound such as LiS. It is considered that the lithium does not contribute to the reversible storage / release reaction. Further, it is considered that the generated compound becomes an obstacle between the hexagonal mesh plane layers and hinders the smooth insertion of lithium ions. These factors reduce charge / discharge efficiency and cycle life.

Further, it is preferable that oxygen, nitrogen, silicon, and metal elements such as Fe and Ni as impurities in the carbonaceous material be as small as possible. Specifically, it is preferable that the oxygen content is 500 ppm or less, the nitrogen content is 1000 ppm or less, and the metal elements such as Fe and Ni are each 50 ppm or less. If these impurity elements exceed the above range, it is conceivable that lithium ions existing between carbon layers react with the impurity elements and are consumed.

Examples of the carbonaceous material of the negative electrode of the present invention include petroleum pitch, coal tar, heavy oil, synthetic pitch,
1500 ° C ~ 3000 using synthetic polymer, organic resin, etc. as raw materials
Coke, carbon fibers, spherical carbon bodies, resin fired bodies, vapor-grown carbon bodies, etc. obtained by firing at a high temperature of ° C. Although the carbonaceous material of the negative electrode according to the present invention is not limited by the production method, a preferred production method will be described below.

First, as a raw material, it is preferable to use a spherical carbon body or short carbon fiber obtained from a high-purity anisotropic pitch produced from coal tar, petroleum pitch or synthetic pitch. High-purity anisotropic pitch has a purity of 95% by volume
Or more, more preferably 98% by volume or more. This is because the isotropic pitch, which is an impurity, causes the collapse of the graphite structure and the generation of amorphous carbon when the carbonaceous material is graphitized. However, when the sintering temperature is as high as 2800 ° C. or more, if the amount of the anisotropic pitch is too large, the graphitization proceeds too much. Although short carbon fibers are used, it is more preferable to use conventional long fibers. This is because it is more advantageous to use short carbon fibers in terms of increasing the production cost and the negative electrode packing density.

The coal tar, petroleum pitch or synthetic pitch preferably has a low sulfur content. Thereby, a graphitized material having few defects in the lattice of the graphite structure can be obtained by heat treatment at a relatively low temperature. In particular, it is preferable to select and use one having a small carbon-sulfur chemical bond in the condensed aromatic carbon constituting the organic substance. This is because the C—S bond accompanied by resonance in the condensed ring is hardly cleaved as compared with the C—S bond in the case where a sulfur atom is present as a part of a substituent, and it is difficult to remove sulfur.
The coal tar, petroleum pitch or synthetic pitch preferably has a low nitrogen content.
In addition, the smaller the proportion of alkyl side chains such as methyl carbon or methylene carbon in the aromatic ring in coal tar, petroleum pitch or synthetic pitch, the more the graphite structure develops,
A carbonaceous material having a large value of (La) by line diffraction can be obtained. However, if (La) is too large, it is not preferable in terms of negative electrode performance.

The high-purity anisotropic pitch includes a mesophase pitch. Spherical carbon bodies and short carbon fibers obtained from mesophase pitch have orientation,
The orientation may be radial, lamellar, or Brooks-Taylor type, but may be any one.

On the other hand, when a spherical carbon body using mesophase pitch as a raw material is used, when extracting mesophase spherulites from coal tar, a treatment for removing minute mesophase spherulites having a particle size of 0.5 μm or less may be performed. It is valid.
Alternatively, heat treatment may be performed at 300 ° C. to 700 ° C. in an oxygen atmosphere to burn out the fine mesophase spherulites or the surface layer attached to the mesophase spherulites. This makes it possible to remove a carbonaceous substance or a graphitized substance that hinders the insertion / desorption reaction of lithium ions, thereby improving the cycle life.

Further, in order to obtain a carbonaceous material having a small amount of impurities such as sulfur as described above, it is preferable to remove impurities during the production of the carbonaceous material. In order to remove sulfur or a sulfur compound from the carbon raw material, heat treatment is performed by allowing a Lewis acid such as CuCl ₃ or chlorine gas or metallic sodium to act at a temperature of 2000 to 3000 ° C., more preferably 2300 to 2800 ° C. There is a way to do it. The heat treatment is preferably performed simultaneously with or after the heat treatment for carbonizing or graphitizing the carbon raw material.

The above-described production method may be applied to the production of the carbonaceous material of the negative electrode according to the present invention using coke as a raw material in addition to the high-purity anisotropic pitch. However, it is preferable that the shape of the obtained carbonaceous material is not a thin side, but a granular or spherical powder using a ball mill or the like at the time of pulverization.

The carbonaceous material constituting the negative electrode according to the present invention is:
As described above, (1)
01) and the diffraction peak (P ₁₀₁₎ (100) peak intensity ratio of the diffraction peak _{(P 100) (P 101 /} P 100), (L
It is preferable to use a), (Lc) and the like within a certain range. A particularly preferred production method for obtaining such a carbonaceous material is described below. The carbon fiber powder obtained from the high-purity anisotropic pitch can be obtained by performing the following treatment.

First, using mesophase pitch as a raw material,
After spinning into a short fiber having a fiber length of 200 to 300 μm by a melt blow method, the mixture is infusibilized and carbonized to a degree that can be pulverized.
The heat treatment for carbonization is 600 to 2000 ° C, preferably 800 to 2000 ° C.
1500 ° C. Plane spacing (d ₀₀₂ ) of (002) by X-ray diffraction of the carbonized mesophase pitch carbon fiber.
Is at least 0.344 nm, more preferably at least 0.357 nm.
The carbon fibers within this range are suitable for grinding. This is because it has a carbon fiber microstructure suitable for shortening the fiber length. On the other hand, (d ₀₀₂ ) is 0.344 nm
When pulverized with less than 10 carbon fibers, the fibers are vertically cracked, and it is difficult to shorten the fiber length. Next, the carbon fiber subjected to the carbonization and pulverization treatment is heat-treated at a temperature of 2000 ° C. or more to be graphitized.

According to this production method, an effect of graphitizing amorphous carbon generated by pulverization or carbon having a low degree of graphitization can be obtained, and the fiber length distribution can be adjusted to 90% or more in the range of 0.5 to 100 μm. Become. As a result, the negative electrode packing density is 1.35 to 1.
It can be in the range of 80 g / cm ³ . In addition, decomposition of the electrolyte solvent accompanying the lithium ion insertion reaction is reduced, and the charge / discharge efficiency is increased to 90% or more.

In the production by the above-mentioned method, the carbonaceous material obtained has a fiber length distribution in the range of 0.5 μm or more and 100 μm or less at 90% by volume and an average fiber diameter of 1 μm or more and 30 μm or less. Preferably, pulverization is performed by selecting appropriate pulverization conditions so that the fine particles having a fiber length of 0.5 μm or less are reduced to 5% by volume or less in the particle size distribution, or sieving is performed after the pulverization. The pulverization and sieving are preferably performed in the air or in an inert atmosphere. In addition, the heat treatment for carbonization and graphitization after pulverization in the above production method is preferably performed in an argon gas stream. The heat treatment temperature for graphitization after grinding in the above manufacturing method is 20
00 ° C or higher, preferably 2000 ° C to 3000 ° C. The heat treatment time may be in the range of 0.5 hours to 30 hours. The distribution of the fiber length and the average fiber diameter of the carbon fiber powder after graphitization are less than the above range by less than 10%.

On the other hand, the positive electrode active material of the lithium secondary battery according to the present invention includes a lithium metal compound mainly composed of at least one metal selected from cobalt, nickel, manganese, vanadium, titanium, molybdenum and iron. Specifically, various oxides such as lithium-manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt compound, lithium-containing nickel-cobalt oxide, amorphous vanadium pentoxide containing lithium, and titanium disulfide And chalcogen compounds such as molybdenum disulfide. Among them, lithium cobalt oxide (LiCoO ₂ ) and lithium nickel oxide (L
iNiO ₂ ), lithium manganese oxide (LiMn ₂ O)
₄ , LiMnO ₂ ) is preferable because of high voltage.

As the solvent of the non-aqueous electrolyte according to the present invention, a known non-aqueous solvent as a solvent for a lithium secondary battery can be used, and there is no particular limitation. It is preferable to use a non-aqueous solvent mainly composed of a mixed solvent with one or more non-aqueous solvents having a melting point lower than that of ethylene carbonate and having a donor number of 18 or less (hereinafter referred to as a second solvent). The non-aqueous solvent having this configuration has the advantage that it is stable with respect to the carbonaceous material having a developed graphite structure, does not easily undergo reductive decomposition or oxidative decomposition of the electrolytic solution, and has high conductivity.

A non-aqueous electrolytic solution using a single solvent of ethylene carbonate has an advantage of being hardly reductively decomposed to a graphitized carbonaceous material, but has a high melting point (39 ° C.
(40 ° C) Due to its high viscosity, it has low conductivity and is not suitable for secondary batteries that operate at room temperature. The second solvent to be mixed with the EC is E
The conductivity is improved by making the viscosity smaller than C, and the EC is easily solvated selectively with lithium ions by making the number of donors 18 or less, and the carbonaceous material having a developed graphite structure can be used. It is considered that the reduction reaction of the second solvent is suppressed. Further, since the number of donors of the second solvent is 18 or less, the oxidative decomposition potential is easily 4 V or more with respect to the lithium electrode, which is advantageous for a high-voltage battery of 4 V or more. The number of EC donors is 16.4.

The more preferred number of donors in the second solvent is 16.5 or less. The viscosity of the second solvent is preferably 28 mp or less at 25 ° C. The mixing ratio of ethylene carbonate as the non-aqueous solvent in the electrolytic solution is preferably from 10 VOL% to 80 VOL%. If the ratio is outside this range, the conductivity will be reduced or the solvent will be decomposed, and the charge / discharge efficiency will be reduced. A more preferred range is 20 VOL
% To 75 VOL%. When the proportion of ethylene carbonate in the non-aqueous solvent is increased to 20 VOL% or more, solvation of ethylene carbonate with lithium ions is facilitated, and the effect of suppressing the decomposition of the solvent is increased.

Examples of the solvent having a lower melting point than ethylene carbonate and a donor number of 18 or less include dimethyl carbonate (DMC) and diethyl carbonate (DE).
C), propylene carbonate (PC), γ-butyrolactone (γ-BL), acetonitrile (AN), nitromethane (NM), nitrobenzene (NB), ethyl acetate (EA), toluene, xylene, or methyl acetate (M
A) and the like. The second solvent to be mixed with ethylene carbonate may have a lower melting point than ethylene carbonate and a mixture of one or more of the above solvents having a donor number of 18 or less. As a more preferable solvent composition, the volume ratio of DEC is preferably 50% or less in a mixed solvent of EC and DEC, EC and PC and DEC, or EC and γBL and DEC. This is a 50% DEC ratio
This is because the followings increase the flash point and improve safety. However, from the viewpoint of further lowering the viscosity, ethers such as diethoxyethane may be added in an amount of 30% by volume or less.

On the other hand, the main impurities present in the non-aqueous solvent as described above include water and organic peroxides such as glycols, alcohols and carboxylic acids. Non-aqueous solvent When used in the electrolyte of the lithium secondary battery of the invention, it is preferable to reduce these impurities as much as possible. Specifically, it is preferable that the water content is 50 ppm or less and the organic peroxide content is 1000 ppm or less. It is considered that these impurities form a poorly conductive film on the surface of the graphitized material and reduce the conductivity of the electrode.
Therefore, there is a possibility that the cycle life and capacity may be reduced. In addition, self-discharge during high-temperature (60 ° C. or higher) storage may increase.

Also, the book Examples of the electrolyte used for the non-aqueous electrolyte according to the present invention include lithium perchlorate (LiClO ₄ ),
Lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiA
sF ₆ ), lithium trifluorometasulfonate (Li
CF ₃ SO _3), bis triflate Oro methylsulfonyl imide _{(LiN (CF 3 SO 2)} 2) lithium salts such as (electrolyte) can be mentioned. Among them, LiPF ₆ , Li
It is preferable to use BF ₄ or LiN (CF ₃ SO ₂ ) ₂ . In particular, a lithium secondary battery using LiBF ₄ or LiN (CF ₃ SO ₂ ) ₂ has a long cycle life and little self-discharge even when operated in a high temperature environment (45 ° C. or higher). This is considered because the chemical reactivity of the electrolyte with the positive electrode or the negative electrode was extremely low.

The amount of the electrolyte dissolved in the non-aqueous solvent is as follows:
Desirably, it is 0.5 to 2.0 mol / l. In addition, the electrolyte according to the present invention is not limited to the above substances. Next, the configuration of the positive electrode and the negative electrode of the lithium secondary battery according to the present invention will be described. The structure of the positive electrode is such that a mixture obtained by mixing the above-described positive electrode active material, a conductive agent, and, if necessary, a binder together with welding is uniformly applied to both surfaces of the current collector. Examples of the current collector used for the positive electrode include a metal foil having a thickness of 10 to 40 μm made of aluminum or an aluminum alloy.

Examples of the conductive agent include carbonaceous materials such as graphite (graphite) and acetylene black. Examples of the binder include an ethylene propylene diene monomer. It is preferable that the mixture of the lithium metal oxide, the conductive agent and the binder contains 20% to 5% by weight of the conductive agent and 5% to 1% by weight of the binder. In the mixture present on both surfaces of the current collector, the ratio of the thickness of the mixture existing on one surface to the thickness of the mixture existing on the other surface is preferably in the range of 1: 1 to 1: 1.2. .

On the other hand, the structure of the negative electrode is such that a mixture of the carbonaceous material and the binder is applied to both surfaces of the current collector. Examples of the current collector used for the negative electrode include a metal foil having a thickness of 5 to 20 μm made of copper, nickel, stainless steel, or the like.

Examples of the binder include carboxymethyl cellulose and styrene butadiene rubber. The binder is 3% by weight in the mixture of the carbonaceous material and the binder.
To 1% by weight. In the mixture present on both surfaces of the current collector, the ratio of the thickness of the mixture existing on one surface to the thickness of the mixture existing on the other surface is 1: 1.
It is preferably in the range of １ ： 1: 1.2.

Book In the invention, the ratio of the thickness of the positive electrode to the thickness of the negative electrode is 2: 1 to 0.9: 1. At this time, the thickness of the positive electrode and the thickness of the negative electrode are the thickness of the coating layer excluding the current collector.

When the thickness of the positive electrode is smaller than the above ratio, the battery capacity is reduced. On the other hand, when the thickness is larger than the above ratio, the cycle life is deteriorated and the charge / discharge rate characteristics of the battery are deteriorated. In this range, the utilization rate of the positive electrode active material increases,
Battery capacity and cycle life are improved. Further, the charge / discharge efficiency of the carbonaceous material of the negative electrode is high, and the cycle life can be further increased. Preferred ratios range from 3: 2 to 0.9: 1.

The book In the present invention, the packing density of the negative electrode is desirably 1.35 to 1.80 g / cm ³ . Outside this range, a decrease in battery capacity and a decrease in the utilization of the positive electrode and the negative electrode occur. More preferable packing density is 1.40 to 1.60 g /
cm ^3.

On the other hand, the packing density of the positive electrode is 2.5 to 4.0 g / cm.
It is desirable to be ³ . Here, the packing density of the positive electrode and the negative electrode indicates the weight per unit volume of each electrode excluding the current collector. Further, in the second invention of the present application, the amount of the non-aqueous electrolyte needs to be 7 cm ³ or less per 1 Ah of battery discharge capacity. Here, the battery discharge capacity indicates a nominal capacity. The amount of electrolyte is important in determining the cycle life, battery capacity and safety of the battery. In the lithium secondary battery using the positive and negative electrodes according to the present invention, since the charge and discharge efficiency of the negative electrode carbonaceous material is high from the first cycle, the decomposition of the electrolytic solution is very small. Therefore, it suffices if there is a sufficient amount of liquid to permeate the separator, the positive electrode, and the negative electrode, and an excessive amount of electrolyte is not required.

In the present invention, when the amount of electrolyte exceeds the above range,
Safety is reduced due to the large amount of electrolyte. On the other hand, the amount of the electrolytic solution permeating into the separator and the positive electrode / negative electrode is not particularly limited because it depends on the thickness of the separator and the porosity of both electrodes, but may be 2 cm ³ / Ah or more. However, in this case, the thickness of the separator needs to be 50 μm or less. If the thickness exceeds this, the strength of the separator increases, but the amount of the electrolyte exceeds the range of the present invention. A more preferred separator thickness is in the range of 30 to 40 μm. If it is less than this range, the amount of the electrolytic solution will decrease, but it is not preferable because the shortage of the positive electrode and the negative electrode and the safety at high temperatures are reduced.

Also, the book In the lithium secondary battery according to the present invention is, then the electrode area width and length of the product of the positive electrode is preferably in the range of 125cm ² ~500cm ² the battery discharge capacity 1 Ah. When it is smaller than this range, the positive electrode utilization rate decreases and the discharge capacity decreases. On the other hand, if it is larger than this range, the thickness of the electrode becomes too thin, so that the packing density of the positive electrode decreases, and the discharge capacity decreases, which is not preferable.

On the other hand, the electrode area of the negative electrode (product of width and length)
Is preferably in the range of 130 to 500 cm ² with respect to the battery discharge capacity of 1 Ah, and preferably has an area equal to or greater than both electrode areas of the opposed positive electrodes. When it is smaller than the above range, the negative electrode utilization rate decreases, so that the discharge capacity decreases. On the other hand, if it is larger than the above range, the thickness of the electrode becomes too thin, so that the packing density of the negative electrode decreases and the mechanical strength of the electrode decreases, which is not preferable.

The battery discharge capacity means a nominal capacity. Further, in the present invention, the ratio of the weight per unit area of the positive electrode (the weight of the positive electrode excluding the current collector) to the weight per unit area of the negative electrode (the weight of the positive electrode excluding the current collector) is 4: 1.
２2: 1. If the weight of the positive electrode exceeds the above ratio, the amount of lithium inserted into the carbonaceous material of the negative electrode becomes excessive, lithium metal is deposited on the negative electrode surface, and cycle deterioration occurs. In addition, since the negative electrode carbonaceous material of the present invention has high charge / discharge efficiency and excellent reversibility, it does not require an excessive amount of the positive electrode active material exceeding the above ratio. On the other hand, when the weight of the positive electrode is smaller than the above ratio, the positive electrode capacity becomes small, the battery capacity decreases, and the cycle deterioration of the positive electrode increases. Therefore, the ratio of the weight per unit area of the positive electrode to the weight per unit area of the negative electrode needs to be within the above range.

[0064]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to an example in which the present invention is applied to a cylindrical lithium secondary battery. Example 1 FIG. 1 shows a configuration of a cylindrical lithium secondary battery used in this example. In FIG. 1, reference numeral 1 denotes a bottomed cylindrical stainless steel container having an insulator 2 disposed at the bottom. In this container 1, an electrode group 3 is housed. The electrode group 3 has a structure in which a band formed by laminating a positive electrode 4, a separator 5 and a negative electrode 6 in this order is spirally wound so that the negative electrode 6 is located outside.

The positive electrode 4 was prepared by mixing 91% by weight of lithium cobalt oxide (LiCoO ₂ ) powder as a positive electrode active material with 3.5% by weight of acetylene black, 3.5% by weight of graphite, and 2% by weight of ethylene propylene diene monomer powder, and adding toluene. The mixture into aluminum foil (thickness
30 μm) It was applied after applying an equal amount to both sides of the current collector and then pressing. The thickness of the positive electrode excluding the current collector is 270μ
m, the weight per unit area of the mixture applied to one surface of the current collector was 378 g / m ² .

The negative electrode 6 is made of a carbonaceous material 9 obtained by a method described later.
A mixture obtained by mixing 6.7% by weight of styrene butadiene rubber with 2.2% by weight of carboxymethyl cellulose and 1.1% by weight of carboxymethylcellulose was applied to both surfaces of a current collector copper foil (thickness: 10 μm) in an equal amount. Negative electrode thickness excluding current collector is 180μ
m. The weight of the mixture applied to one side of the current collector is 1
It was 40 g / m ² . Therefore, the ratio of the thickness of the positive electrode to the negative electrode excluding the current collector is 1.5 : 1, and the weight ratio per unit area is
2.7: 1. The packing density of the negative electrode was 1.56 g / cm2.

In the container 1, LiPF ₆ is filled with EC and P
Mixed solvent of C and DEC (mixed volume ratio 1: 1: 1) 1.0
3.85 cm ^{3 of} a non-aqueous electrolyte having a composition dissolved at a concentration of mol / l
Is housed. The number of DEC donors is 16. The amount of H ₂ O in the non-aqueous electrolyte was 20 ppm.

On the electrode group 3, an insulating paper 7 having an opening at the center is placed. Further, an insulating sealing plate 8 is provided in the upper opening of the container 1 in a liquid-tight manner by caulking the container 1 or the like, and a positive electrode terminal 9 is fitted in the center of the insulating sealing plate 8. Have been. This positive electrode terminal 9
Is connected to the positive electrode 4 of the electrode group 3 via a positive electrode lead 10 made of aluminum. The negative electrode 6 of the electrode group 3 is connected to the container 1 as a negative electrode terminal via a negative electrode lead (not shown) made of copper.

The carbonaceous material was obtained by the following method. First, the purity of anisotropic pitch obtained from petroleum pitch is 100
% Mesophase pitch as a raw material, the pitch was spun into short fibers, and further heat-treated at 1000 ° C. in an argon atmosphere to carbonize to obtain mesophase pitch-based carbon fibers. The (d ₀₀₂ ) of the mesophase pitch-based carbon fiber measured by X-ray diffraction was 0.360 nm. The average fiber diameter was 12 μm. The obtained carbon powder is formed so that the obtained carbon powder has a fiber length distribution of 0.5 to 80 μm.
After appropriately pulverizing so that 90% by volume was present, it was graphitized at 3000 ° C. in an argon atmosphere.

The obtained carbonaceous material is a graphitized carbon powder having an average fiber diameter of 11 μm, and has a fiber length distribution of 90 to 90 μm.
% By volume was present. In addition, the specific surface area by N ₂ gas adsorption BET method was 8 m 2 / g.

When various parameters were measured by the half-width half-point method by X-ray diffraction, the value of (P ₁₀₁ / P ₁₀₀ ) was 1.
It was 0. (D ₀₀₂ ) is 0.3375 nm, (Lc) is 21 nm,
(La) was 40 nm. The exothermic peak determined by differential thermal analysis in air was 870 ° C. Further, the content of sulfur in the carbonaceous material was 100 ppm or less. Other oxygen content is 100 ppm or less, nitrogen content is 100 ppm or less, F
e and Ni were each 1 ppm.

The above (P ₁₀₁ / P ₁₀₀ ), (d ₀₀₂ ),
Table 1 shows (Lc), (La), differential thermal peak temperature, positive electrode / negative electrode thickness ratio, positive / negative electrode weight ratio, positive electrode material, negative electrode packing density, and electrolyte amount.

[0073]

[Table 1] (Example 2) An electrode similar to that of Example 1 was assembled except that the thickness and the weight of the positive electrode and the negative electrode were as shown below.

The thickness of the positive electrode excluding the current collector was 245 μm, and the weight per unit area of the mixture applied to one surface of the current collector was 3 μm.
It was 40 g / m ² . The thickness of the negative electrode excluding the current collector is 220μ
m, the weight per unit area of the mixture applied to one surface of the current collector was 150 g / m ² . The packing density of the negative electrode is 1.43 g /
It was cm ^3.

Therefore, the ratio of the thickness of the positive electrode to that of the negative electrode excluding the current collector is 1.11 : 1, and the weight ratio of the two electrodes per unit area is 2.2.
7: 1. The amount of the electrolyte was 4.0 cm ³ . Example 3 A battery similar to that of Example 2 was assembled except that a positive electrode made of the following positive electrode active material was used.

A lithium nickel oxide (LiNiO ₂ ) was used as a positive electrode active material. The electrolyte is LiN
(CF ₃ SO ₂ ) ₂ was used. The amount of the electrolyte was 4.0 cm ³ . Example 4 A battery similar to that of Example 1 was assembled using the following positive electrode active material except for the thickness and weight of the positive electrode and the negative electrode.

A lithium manganese oxide (LiMn ₂ O ₄ ) was used as a positive electrode active material. The thickness of the positive electrode excluding the current collector was 290 μm, and the weight per unit area of the mixture applied to one surface of the current collector was 390 g / m ² .

The thickness of the negative electrode excluding the current collector was 175 μm, and the weight of the mixture applied to one surface of the current collector was 132 g / m ² . Therefore, the thickness ratio of the positive electrode and the negative electrode excluding the current collector is
1.66 : 1, weight ratio per unit area of both poles 2.95: 1
It is.

The packing density of the negative electrode was 1.60 g / cm ³ . The amount of the electrolyte was 3.6 cm ³ . (Example 5) A battery similar to that of Example 1 was assembled except that a carbonaceous material as shown below was used for the negative electrode.

As the carbonaceous material for the negative electrode, the surface layer was
The mesophase microspheres which had been oxidized and removed by weight% were graphitized at 2800 ° C. In the measurement by X-ray diffraction, (d
₀₀₂ ) is 0.3359 nm, (Lc) is 37 nm, (La) is 66 nm,
(P ₁₀₁ / P ₁₀₀₎ was 2.15. Differential heat peak is 8
At 00 ° C., the sulfur content was 100 ppm. The amount of electrolyte is 4
It was cm ^3. (Example 6) A battery similar to that of Example 4 was assembled, except that the carbonaceous materials shown below were used for the negative electrode, and the thickness and weight of the positive electrode and the negative electrode were the same.

The negative carbonaceous material was obtained by the following method. First, using a 100% pure mesophase pitch obtained from a petroleum pitch as a raw material, the pitch is spun into short fibers, and further heat-treated at 1000 ° C. in an argon atmosphere to carbonize mesophase pitch yarn carbon fibers ((d ₀₀₂ ) Is 0.355 nm)
I got The carbon fibers of the mesophase pitch yarn had an average fiber diameter of 17 μm. The distribution of the fiber length of the carbon fiber is 0.5 to
After appropriately pulverizing so that 90% by volume was present in 60 μm, it was graphitized at 3000 ° C. in an argon atmosphere.

The obtained carbonaceous material had an average fiber diameter of 16 μm.
Is a graphitized carbon powder with a fiber length distribution of 0.5-60 μm
90% by volume. The specific surface area determined by the N ₂ gas adsorption BET method was 4 m ² / g. When various parameters were measured by the half-width half-point method by X-ray diffraction, (P
₁₀₁ / value of P ₁₀₀₎ was 1: 1. (D ₀₀₂ ) is 0.
3368 nm, (Lc) was 21 nm, and (La) was 28 nm. The exothermic peak determined by differential thermal analysis in air was 840 ° C. The content of sulfur in the carbonaceous material was 100 ppm or less. In addition, the content of oxygen was 100 ppm or less, the content of nitrogen was 100 ppm or less, and each of Fe and Ni was 1 ppm.

The thickness of the positive electrode excluding the current collector was 275 μm, and the weight per unit area of the mixture applied to one surface of the current collector was 3 μm.
It was 89 g / m ² . The thickness of the negative electrode excluding the current collector is 190μ
m, the weight per unit area of the mixture applied to one surface of the current collector was 140 g / m ² .

Therefore, the ratio of the thickness of the positive electrode to that of the negative electrode excluding the current collector was 1.45 : 1, and the weight ratio of the two electrodes per unit area was 2.
78 : 1. The negative electrode packing density was 1.56 g / cm ³ .
The amount of the electrolyte was 3.85 cm ³ . (Comparative Example 1) A battery similar to that of Example 1 was assembled using a carbonaceous material as described below for the negative electrode, except for the thickness and weight of the positive electrode and the negative electrode.

Petroleum pitch and coke carbonized at 1400 ° C. were used as the carbonaceous material for the negative electrode. Note that (d)
₀₀₂ ) is 0.350 nm, (Lc) is 4.5 nm, (P ₁₀₁ / P
₁₀₀ ) was 0. The differential heat peak was 703 ° C., and the sulfur content was 1200 ppm.

The thickness of the positive electrode excluding the current collector was 200 μm, and the weight per unit area of the mixture applied on one side of the current collector was 2 μm.
It was 65 g / m ² . The thickness of the negative electrode excluding the current collector is 260μ
m, the weight per unit area of the mixture applied to one surface of the current collector was 150 g / m ² . Therefore, the ratio of the thickness of the positive electrode to the thickness of the negative electrode excluding the current collector is 0.77 : 1, and the weight ratio of both electrodes per unit area is 1.77: 1.

The packing density of the negative electrode was 1.25 g / cm ³ . The amount of the electrolyte was 5 cm ³ . Comparative Example 2 A battery similar to that of Example 5 was assembled except for the thickness and weight of the positive electrode and the negative electrode as described below.

The thickness of the positive electrode excluding the current collector was 320 μm, and the weight per unit area of the mixture applied to one side of the current collector was 4 μm.
It was 20 g / m ² . The thickness of the negative electrode excluding the current collector is 140μ
m, the weight per unit area of the mixture applied to one surface of the current collector was 100 g / m ² , and the negative electrode packing density was 1.38 g / cm ³ .

Accordingly, the ratio of the thickness of the positive electrode to that of the negative electrode excluding the current collector is 2.29 : 1, and the weight ratio per unit area of both electrodes is
4.2: 1. The negative electrode packing density was 1.33 g / cm ³ . The amount of the electrolyte was 2 cm ³ . Comparative Example 3 A battery similar to that of Example 1 was assembled, except for the thickness and weight of the positive electrode and the negative electrode as described below.

The thickness of the positive electrode excluding the current collector was 220 μm, and the weight per unit area of the mixture applied on one side of the current collector was 290.
g / m ² . The thickness of the negative electrode excluding the current collector is 240μ
m, the weight per unit area of the mixture applied to one surface of the current collector was 170 g / m ² .

Therefore, the ratio of the thickness of the positive electrode to that of the negative electrode excluding the current collector is 0.92 : 1, and the weight ratio of the two electrodes per unit area is 1.
71 : 1. The negative electrode packing density was 1.48 g / cm ³ .
The amount of the electrolyte was 5 cm ³ . Comparative Example 4 A battery similar to that of Example 2 was assembled except that a carbonaceous material as shown below was used for the negative electrode.

The carbonaceous material of the negative electrode was obtained by the following method. First, using a 100% pure mesophase pitch obtained from petroleum pitch as a raw material, the pitch is spun into short fibers, and further heat-treated at 2800 ° C. in an argon atmosphere to obtain a graphitized mesophase pitch yarn carbon fiber (d _002). ) Is 0.339nm,
(Lc) is 18 nm, (La) is 30 nm, (P ₁₀₁ / P ₁₀₀ )
Got 0.6. The carbon fiber is crushed and the fiber length distribution is
20 volume% exists in 0.5 to 100 μm, and the average fiber length is 150
μm. The average fiber diameter was 4 μm. Also N ₂
The specific surface area determined by the gas adsorption BET method was 1.2 m ² / g. The weight per side excluding the negative electrode current collector is 120 g
/ M ² , thickness 190μm, negative electrode packing density 1.33g / cm
^{Was 3} .

Thus, the lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 4 were charged at room temperature for 400 hours at a charging current of 400 mA to 4.2 V for 3 hours.
Charge / discharge of discharging at 400 mA to V was repeated, and (discharge cycle test) discharge capacity and cycle life were measured. The result is shown in FIG.

As is apparent from FIG. 2, the lithium secondary batteries of Examples 1 to 6 have larger capacities and significantly improved cycle life as compared with the batteries of Comparative Examples 1 to 4. Understand.

Further, the battery of Example 3 was operated at a battery operating condition of 60 ° C., and the same cycle characteristics test as in Example 1 was performed to measure the cycle life. The capacity after 300 cycles of operation was about 80% of the capacity of the battery that was cycled the same number of times at room temperature. For comparison, LiPF was used as the electrolyte.
A battery similar to that of Example 3 was prepared except that No. ₆ was used, and a similar cycle test was performed at room temperature and 60 ° C. 30
The capacity after the zero cycle operation was about 50% of the capacity of the battery operated at the same number of times at room temperature.

On the other hand, in all the examples, EC / PC / DEC (1: 1: 1) was used as a solvent for the electrolytic solution.
C, / DEC (1: 1), EC / γ-BL (1: 1),
EC / γ-BL / DEC (2: 1: 1) or EC /
Even when a mixed solvent of PC (1: 1) was used, high capacity and long life were obtained as in this example. Similarly, high capacity and long service life were obtained even when 5 VOL% of toluene and m-xylene were added to lower the viscosity.

[0097]

As described above, according to the present invention, a lithium secondary battery having a high capacity and an excellent cycle life can be provided.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a cylindrical lithium secondary battery according to Embodiment 1 of the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the discharge capacity of the lithium secondary batteries of Examples 1 to 6 and Comparative Examples 1 and 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Stainless steel container 3 ... Electrode group 4 ... Positive electrode 5 ... Separator 6 ... Negative electrode 8 ... Sealing plate 9 ... Positive electrode terminal

Continuation of the front page (56) References JP-A-4-332482 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/02-4/04 H01M 4 / 58

Claims (3)

(57) [Claims] 1. A positive electrode comprising, as an active material, a lithium metal compound mainly composed of at least one metal selected from the group consisting of cobalt, nickel, manganese, vanadium, titanium, molybdenum, and iron; 700 ° C by thermal analysis
As described above, the peak intensity ratio (P ₁₀₁ / P ₁₀₀ ) of the (101) diffraction peak (P ₁₀₁ ) and the (100) diffraction peak (P ₁₀₀ ) of the graphite structure having an exothermic peak by X-ray diffraction is 0.7.
A lithium secondary battery comprising a negative electrode containing a carbonaceous material powder of 2.2 or less and a non-aqueous electrolyte, wherein the ratio of the thickness of the positive electrode to the thickness of the negative electrode is 2: 1 to 0.9: 1. ,
And a ratio of the weight per unit area of the positive electrode to the weight per unit area of the negative electrode is from 4: 1 to 2: 1. 2. The packing density of the negative electrode is 1.35 to 1.80 g /
2. The lithium secondary battery according to claim 1, wherein the size of the lithium secondary battery is cm ³ . 3. The lithium secondary battery according to claim 1, wherein the carbonaceous material is mesophase pitch-based carbon fibers or mesophase spherules.